1. Field of the Invention
The present invention is generally related to transformers, and more specifically, to an efficient, low leakage inductance, multi-tap, RF transformer.
2. Discussion of the Background
A transformer is a device that transfers electrical energy from one circuit to one or more other circuits, either increasing (stepping up) or decreasing (stepping down) a voltage. A transformer transfers energy through the process of electromagnetic induction.
A conventional transformer includes a first coil (the primary winding) and a second coil (the secondary winding). The primary winding and the secondary winding of a transformer are placed in close proximity to each other so that when a varying flux is produced in the primary winding the varying flux passes through the secondary winding. A varying flux can be produced in the primary winding by applying a varying voltage to the primary winding. As a result of the varying flux passing though the secondary winding, a voltage will be developed across the secondary winding through the process of electromagnetic induction. In this manner, voltage is transferred from the primary winding to the secondary winding.
FIG. 1 is an illustration of an ideal transformer 100. As shown in FIG. 1, transformer 100 includes a first coil 101 and a second coil 102. The first coil 101 is placed in close proximity to the second coil 102. The first coil 101 will be referred to as the primary winding 101 and the second coil 102 will be referred to as the secondary winding 102. Because transformer 100 is an ideal transformer (that is, it is 100% efficient), the relationship between the varying voltage developed across the secondary winding (Vs) and the varying voltage applied to the primary winding (Vp) is: Vs=Ns/Np (Vp), where Ns is the number of turns in the secondary winding 102 and Np is the number of turns in the primary winding 101.
Unfortunately, unlike ideal transformers, realizable transformers are not 100% efficient. Realizable transformers have a characteristic called xe2x80x9cleakage inductance,xe2x80x9d which generally appears to be in series with the primary winding. The greater the leakage inductance of a transformer, the lower the transformer""s efficiency. Consequently, in applications where high efficiency is demanded, the goal of the transformer designer is to reduce the leakage inductance as far as possible. However, the designs that have been developed to overcome the leakage inductance problem are difficult to manufacture, not versatile, and/or not able to transform energy efficiently over a wide range of frequencies.
Therefore, what is desired is an efficient, versatile, low leakage inductance transformer that is easy and inexpensive to manufacture.
The present invention provides a low leakage inductance, versatile RF transformer with multiple input/output voltage ratios.
In one aspect, a transformer according to one embodiment includes a stack of conductors that has been shaped into the form of coil. A first group of the conductors form the primary winding of the transformer and the remaining conductors form the secondary winding. Preferably, to minimize leakage inductance, the group of conductors that forms the primary winding is interleaved with the group of conductors that forms the secondary winding.
A printed circuit board (PCB) is used to connect the conductors. More specifically, the PCB has a first set of plated slots and traces that are used to interconnect the conductors that form the primary winding, and the PCB has a second set of plated slots and traces that are used to interconnect the conductors that form the secondary winding. In one embodiment, the first set of traces connect in series the conductors that form the primary winding, and the second set of traces connect in series the conductors that form the secondary winding.
Advantageously, the PCB also has a number of input and output terminals (also referred to as thru-holes). The input terminals are connected to the primary winding and the output terminals are connected to the secondary winding.
In another aspect, the present invention provides an auto-transformer. The auto-transformer includes a plurality of conductors stacked on top of each other and formed into the shape of a coil. The auto-transformer also includes a PCB having a plurality of slots and a plurality of traces for electrically connecting the conductors. In one embodiment, the plurality of traces connect the conductors in series. There are also provided a number of input terminals and output terminals so that the user of the auto-transformer can select one from among many possible voltage ratios.